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To respond to the various issues of conventional drying (textural defects of collapse-shrinkage and case hardening, microbiological contamination, poor rehydrability, degradation of active molecules caused by high wet-bulb temperature, weak drying kinetics, and marketing difficulty), swell-drying has proven high relevance in combining conventional drying processes with the Instant Controlled Pressure Drop (D.I.C.). The international team of "Research & Engineering Platform for intensifying Drying Processes (REPID)" has studied phenomenological models and experimental trials combining D.I.C. with new Interval Hyper-Active Drying (IHAD) processes. Currently, IHAD includes interval starting accessibility drying (ISAD), interval infrared airflow drying (IIRAD), and interval microwave airflow drying (IMAD). All these "interval operations" are sandwiched into cycles, each comprising double separate independent mechanisms; a short, hyper-focused active period (that generates and sweeps out vapor to the surrounding environment) alternated by a passive period of internal water diffusion/moisture homogenization. Since surface evaporation is highly intensive, the wet-bulb temperature stays low, although highly effective drying kinetics. Thus, the operation results in avoiding biochemical damage risks. Coupled with the D.I.C. texturing-decontamination, these drying operations are very effective in terms of drying kinetics, energy consumption, and product quality of heat-sensitive solids. It has led to the manufacturing of effective drying equipment. [ABSTRACT FROM AUTHOR]

Partial air-drying, instant controlled pressure drop, freezing, and thawing operations were combined to minimize the texture loss of frozen/thawed apple fruits. Fresh apple samples (700% db) and samples previously dehydrated until different water contents [200, 100, and 30% dry basis (db)] and DIC treated at constant conditions (0.2 MPa, 25 s) were completely frozen at − 30 °C and at two different freezing velocities and then thawed at 4 °C. The effects of sample water content and freezing velocity on freezing/thawing durations and apple texture were assessed. Lower sample water content implied higher freezing and thawing rates, and lower freezing and thawing times. Indeed, freezing times are 108 min and 30 min for samples with water contents of 700% and 100% db, respectively. Thawing time was also reduced from 588 to 42 min for conventionally frozen and DIC-dehydrofrozen samples (100% db). During thawing, the amount of water exudate was approximately 12% (g/100 g residual water) for conventionally frozen apples at the lower freezing velocity. Whereas, it is lowered to 1.6% for 100% db DIC-dehydrofrozen samples. Moreover, the impact of freezing velocity on water exudate was significant and very important only for conventionally frozen apples (with high water content) and remains insignificant for DIC-dehydrofrozen samples with different water content levels. Thawed apple firmness was as higher as the water content was lower, without any significant impact of freezing velocity. Dehydrofreezing assisted by instant controlled pressure drop exhibited significant effects on reducing thawing duration and enhancing frozen apple fruit texture. [ABSTRACT FROM AUTHOR]

Dehydrofreezing process involves water partial removal before freezing. This treatment has been proposed in order to reduce the negative impacts of conventional or even accelerated freezing, especially on the textural quality of high water content fruits and vegetables. Indeed, in such cases, freezing and thawing processes result in severe damage of the integrity of product's cell structure due to the formation of ice crystals. For this purpose, quince fruits (7 g H2O/g db) were subjected to convective air drying of 40 °C and 3m/s to reach different water content levels of 2, 1, and 0.3 g H2O/g db. Freezing profiles obtained at various freezing rates (V1, V2, and V3) for different water contents allowed the main freezing characteristics such as the Initial Freezing Temperature (IFT), the Practical Freezing time (PFt), and the Specific Freezing time (SFt) to be assessed. The impact of freezing rate was important on PFt and SFt, and more pronounced for high water contents (W between 7 and 2 g H2O/g db (dry basis)). Furthermore, IFT decreased sharply when initial sample water content decreased. Indeed, it started at −0.8 °C for W = 7g H2O/g db, while it reached a value of −8.2 °C for samples of W = 1g H2O/g db. Since convective air drying normally triggers shrinkage which causes a detrimental deformation of fruit structures, instant controlled pressure drop (DIC) treatment was used to improve the texture and enhance the whole dehydrofreezing performance and the final frozen-thawed product quality. Moreover, DIC implied a slight increase of PFt compared to untreated ones. On the other hand, quality attributes were estimated through the assessment of thawed water exudate (TWE g H2O/100 g db), color and texture (maximum puncture force as index of firmness): freezing rate and water content had great impacts on TWE. Hence, the lower the water content, the weaker the TWE. Furthermore, the TWE of the pre-dried quince (0.3 g H2O/g db) had higher value for DIC-textured samples than for the un-treated ones. Indeed, DIC-texturing leads to a well-controlled structure expansion of the cell wall. These textural changes resulted in more lixiviation of residual water. Consequently, water becomes more available, hence more releasable after thawing. Finally, the partial removal of water by air drying before freezing remarkably reduced the negative impact of freezing/thawing processes on final quince color. Decisively, the firmness of quince fruit increased with the decrease of water content level. Abbreviations: DMC: Dry Matter Concentration (%); DIC: Instant controlled pressure drop; W: Water content dry basis (g H2O/g db); IFT: Initial Freezing Temperature (°C); PFt: Practical Freezing time (min); SFt: Specific Freezing time (min); TWE: Thawed Water Exudate (g H2O/100 g db); L, a, and b: Color coordinates; (L): The degrees of lightness; (a) and (–a): The redness (a) or greenness (−a), respectively; (b) and (−b): The yellowness (b) or blueness (−b), respectively; ΔE*ab: Total color difference; L0, a0, and b0: Color coordinates of fresh or dried quince samples; SD: Standard Deviation; ANOVA: Analysis of variances; LSD: Least Significant Differences; cp: Specific Heat of the product depending on composition (dry material and water content)(KJ/kg K); cpd: Specific Heat of the dry material (KJ/kg K); cpW: Specific Heat of water (KJ/kg K); V1: Freezing rate without insulation; V2: Freezing rate with a food stretch film insulation with thickness e2 = 3 mm and thermal conductivity λ2 = 0.17 W/m K; V3: Freezing rate with a versatile flexible insulation (Armacell) with thickness e3 = 13mm and weak thermal conductivity λ3 = 0.036 W/m K; vd: Volume of dry material of quince sample (mm3); vH2O: Volume of quince sample water (mm3); vt: Total volume of quince sample (mm3); e0: Quince sample thickness (mm); e2: Insulation thickness in the case V2; = 3 mm; ; e3: Insulation thickness in the case V3; = 13 mm; ; λ0: Quince sample conductivity (W/m K); λ2: Insulation conductivity in the case V2; = 0.17 W/m K; ; λ3: Insulation conductivity in the case V3; = 0.036 W/m K; λd: Conductivity of quince sample dry material (W/m K); λH2O: Conductivity of water (W/m K); λequiv: Equivalent conductivity of quince sample versus water content (W/m K); mi and mf: Weights of the frozen and thawed samples, respectively [ABSTRACT FROM AUTHOR]

The aim of this research work was to compare the effect of different apple processing methods on textural properties at equal water content (100% db dry basis). Pre-dried samples were treated by instant controlled pressure drop (DIC), completely frozen and thawed. In order to reach a final water content level of 100% db, the samples were post dried or rehydrated. DIC and freezing increased drying and rehydration rates. A combination of DIC and freezing showed less important effects on sorption isotherms and drying/rehydration kinetics. Freezing had significant detrimental effect on firmness for high initial water content samples. This effect disappeared and firmness kept constant regardless of the initial water content once sample initial water content is lower than 115% db. Significant initial water content effect appeared after freezing/thawing for DIC untreated samples. However, by inserting DIC prior to freezing, the textural effect of final water content became insignificant after freezing/thawing. [ABSTRACT FROM AUTHOR]